The drying of such products is useful for a multi-sector recycling of the dried products, in particular for:                long-term storage without fermentation;        simple agricultural recycling that is acceptable to the population, owing to a “sanitized” product;        an advantageous thermal recycling.        
But the drying technology is accompanied by several impediments, in particular:                its high energy consumption, mainly based on fossil energy;        the complexity of storing organic dried products that may readily self-combust.        
A sludge ultra-dehydrated to at least 50% dryness and preferably to 65% or more dryness has the advantages of:                absence of self-combustion during storage;        while retaining an advantageous thermal recycling;        sanitization of the product.        
Dryers that currently exist, of direct or indirect type, may require, for the drying of the sludge, an energy of around 900-1100 kWh/TWE (tonne of water evaporated).
Systems of dryers with pre-evaporation of the sludge make it possible to obtain lower consumptions, of around 700-800 kWh/TWE.
Dryers that use heat pumps claim purely electrical consumptions of 300 kWhe/TWE (kWhe=kilowatt-hour electrical), which amounts to an equivalent of around 900 kWh/TWE in terms of thermal energy.
Dryers that use mechanical steam compression claim thermal consumptions of less than 300 kWhe/TWE, but mechanical steam compression technology has not displayed industrial implementability.
Furthermore, thermal conditioning of pasty products, and of sludge in particular, has displayed an ability to substantially improve the dryness of a sludge by filter press dehydration. Thermal conditioning consumes little energy, in particular when it is used on pasty and non-liquid products since it does not carry out evaporation of water but only a heating. There is therefore no noticeable heat loss.
One drawback of filter presses lies in the disassembling operation which consists in discharging the filter cake from the press. This filter press operation generally requires a manual intervention, and the automation thereof is difficult, if not impossible. The pressing and disassembling operation of a conventional plate filter press is accompanied by the release of odors into the atmosphere.
Moreover, the method of drying with thermal conditioning and filter press is accompanied by problems of integration of the procedure for producing ultra-dehydrated sludge regarding in particular:                the total energy consumption for producing a sludge ultra-dehydrated to at least 50% dryness;        the management of the odors over the whole of the treatment train;        the automation of the treatment train;        the ability to manage and store ultra-dehydrated sludge.        